CHAPTER 6LESSON B

Creating Custom Forms

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Lesson B Objectives Suppress default system messages Create alerts and messages to provide

system feedback to users Create applications that avoid user

errors Trap common runtime errors

3 Controlling System Messages

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Controlling System Messages By default, FRM- and ORA- messages are

displayed in the Forms Services message line

They are useful for determining : If the DBMS successfully inserts, updates,

or deletes a record The nature of errors that occur while the

form is running

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Controlling System Messages Oracle classifies system messages

according to: their severity Whether or not they require user

intervention

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System message severity levelsMessage Severity Level

Description Example

5 Informative message that doesn’t require user intervention

FRM-40400: Transaction complete: 1 records applied and saved

10 Informative message that identifies a procedural mistake made by the user

FRM-40201: Field is full: Can’t insert character

15 Informative message that identifies a data-entry error, such as entering an incorrect data value in a text item

FRM-50016: Legal characters are 0-9 - + E

20 Error message that identifies a condition that keeps a form trigger from working correctly

FRM-40602: Can’t insert into or update data in a view

25 Error message that identifies a condition that causes the form to operate incorrectly

FRM-40919: Internal SQL statement execution error: %d

>25 Error message that identifies a condition that must be corrected immediately for the form to continue running

FRM-40024: Out of memory

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System message severity levels Form developers can set

the :SYSTEM.MESSAGE_LEVEL to suppress error messages equal to or less than a certain level

By default, the :SYSTEM.MESSAGE_LEVEL is 0, so all messages are displayed

The variable is commonly set in the PRE-FORM trigger

8 Providing System Feedback

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Providing System Feedback It is important for a Forms Builder

application to provide feedback to users. Feedback can be provided via the form

message line or through the use of an alert.

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Custom Messages A custom message is a short (up to

200 characters) text string that the form developer displays on the form message line

The MESSAGE built-in is used to display a custom message. The syntax is:

MESSAGE('message_string');

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Alerts An alert is a pop-up dialog box or

window that displays a message and buttons

We need alerts when: The feedback requires a longer message

than will fit on the message line The user needs to select between alternate

ways to proceed Or, the user needs to acknowledge

important messages

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Creating an Alert To create a new alert:

Select the Alerts node in the Object Navigator

Click on the create button Specify the alert properties

An alert can have a maximum of three buttons

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Alert Styles1. Note alert

display an “i” for information Conveys information to the user, such as confirming that the

form has inserted a record2. Caution alert

display an exclamation point “!” Inform the user that he is about to make a choice that can’t be

undone and could lead to a potentially damaging situation, such as deleting a record

3. Stop alert display a red “X” or a red stoplight Inform the user that he has instructed the system to perform

an action that is not possible, such as trying to delete a record that is referenced as a foreign key another table

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Displaying an Alert To display an alert in a form, you use the

SHOW_ALERT built-in function The SHOW_ALERT function returns a

numeric value indicating which button the user pressed.

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Displaying an Alert To display an alert during the execution

of a trigger, you need to: declare a numeric variable Assign to this variable the value that the

SHOW_ALERT function returns using the syntax:DECLARE

alert_button NUMBER;BEGIN

alert_button := SHOW_ALERT (‘alert_name’);END;

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Displaying an Alert To execute alternate program commands

depending on the alert button that the user clicks, we create an IF/ELSEIF decision control structure

This structure: Evaluates the value that the SHOW_ALERT

function returns Executes the appropriate program

command

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Displaying an Alert Syntax to display an alert and execute alternate

commands depending on the button the user clickedDECLARE

alert_button NUMBERBEGIN

alert_button := SHOW_ALERT (‘alert_name’);IF alert_button = ALERT_BUTTON1 THEN

commands to execute for second alert buttonELSEIF alert_button = ALERT_BUTTON2 THEN

commands to execute for first alert buttonELSEIF alert_button = ALERT_BUTTON3 THEN

commands to execute for third alert buttonEND IF;

END;

18 Avoiding User Errors

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Avoiding User Errors A properly designed form can help users

avoid errors Techniques include validating user input,

disabling command buttons, and disabling text items

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Validating Form Input Values When a user enters a value in a text item, it

can be validated against business rules to determine whether the user made a data entry error

Text item validation can be performed using text item validation properties or validation triggers

A form can validate a text item’s value using specific text item validation properties that can be used in data block or custom forms

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Text Item Validation PropertiesProperty Node

Property Allowable Values Description

Data Data Type Char, Number, Date, Alpha, Integer, Datetime, Long, Rnumber, Jdate, Edate, Time

Ensure that input values are of the correct data type

Data Maximum Length

Integer value Defines the maximum number of characters the item will accept

Data Required Yes or No Specifies whether or not the value can be NULL

Data Lowest Allowed Value

Integer value For numerical fields, specifies the lowest acceptable value

Data Highest Allowed Value

Integer value For numerical fields, specifies the highest acceptable value

Data Format Mask Legal format masks Ensure that user input is in the correct format

List of Values

Validate Form List

Yes or No Specifies that the value entered by the user should be validated against the item’s LOV

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Validation Unit The level at which form validation occurs

is called the validation unit It can be set to validate a field whenever

the user navigates away from the field; this is the default

Other possible values are Form, Data Block, and Record

However, for a custom form, validation should be performed at the Item level.

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Form Validation Trigger Text item validation properties work well

for simple validation, but more complex validation can be coded in an item validation trigger

This is an item-level trigger associated with the WHEN-VALIDATE-ITEM event.

If the item does not satisfy the validation rules coded in the trigger, the form displays a message and raises a FORM_TRIGGER_FAILURE exception

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Disabling Form Command Buttons to Avoid User Errors It is a good idea to disable any button that

should not be pressed at a particular time. Example: in a form to enter student data, the

Save New button should be disabled until the student’s last name is entered

The method used to disable a button is:SET_ITEM_PROPERTY('item_name‘, property_name,property_value);

In the case of disabling a button, property_name is ENABLED, and the value should be FALSE to disable the button and TRUE to enable it.

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Disabling Text Item Navigation When a form displays certain items such

as primary keys, it is a good idea not to allow the user to modify the value

One way to do this is to prevent navigation to the field by making it nonnavigable

This means that the user cannot use the Tab key to navigate to the text item

To make an item nonnavigable, set the Keyboard Navigable property to No.

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Disabling Text Item Navigation Since the user can still navigate to the

item using the mouse, it is also necessary to create a trigger that moves the form focus away from a text item whenever the mouse is placed there

The WHEN-MOUSE-UP event can be used to activate this trigger

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Trapping Form Runtime Errors The ON-ERROR event occurs when FRM-

and ORA- messages are generated There are four built-in procedures used

for obtaining information about runtime errors

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Forms Builder Built-in Procedures for Handling Errors

Procedure Name Data ReturnedDBMS_ERROR_CODE Error number of the most recent database

(ORA) error, represented as a negative integer

DBMS_ERROR_TEXT Error number and message text of the most recent ORA- error

ERROR_CODE Error number of the most recent Forms Services (FRM) error, represented as a positive integer

ERROR_TEXT Error number and text of the most recent FRM- error or message